A Kinetic Model of Coordinated Myosin V

We present a kinetic model for the walking of myosin V on actin under conditions of zero external force. The model includes three pathways and the termination of the processivity. Exptl. measured kinetic parameters are used in the model to obtain quant. results. Using the model and assocd. parameters, we compute the proportion of the pathway contg. an intermediate state, as well as the walking velocities and run lengths at various concns. of ATP and ADP. The resulting trends agree with exptl. data. The model explains the surprising exptl. finding that myosin walks at a faster speed but for a shorter distance as the ATP concn. increases in the absence of ADP. It also suggests that under physiol. condition ([ADP] ∼ 12-​50 μM)​, myosin walks with a higher speed and for longer distances when ATP is more abundant.